Birders and botanist join forces to shed new light on an age-old riddle of avian migration

Mark Alvery

Please note: this news story, recovered on 28-Jan-2017, was originally published in Science Dialogues on 5-Sept-2014.

A team from the University of Chicago, The Field Museum, and the University of Minnesota has been working for three years on a topic that has long confounded avian biogeographers: the origins and evolution of bird migration. In the August 19 issue of Proceedings of the National Academy of Sciences the team—U of C Ph.D. student Ben Winger, FMNH Associate Curator Rick Ree, and Minnesota prof Keith Barker—published a paper aimed at resolving that question for one of the largest groups of migratory birds.

Ben Winger measuring specimens in the Field Museum Bird collections.

Traditionally, there have been two schools of thought on where migration began and how it evolved: one theory proposed that ancestors of migratory birds spent the whole year in temperate regions, and that migration patterns evolved over time as these birds’ winter ranges gradually moved to the tropics. The other theory held that these ancestors were originally found in the tropics, with breeding grounds shifting to more temperate locales like North America.

To solve this riddle of migration the team used an innovative phylogenetic model designed to infer the historical biogeography of migratory birds. Ben and Rick developed this new model based on an existing biogeographic method that Rick developed called the “dispersal-extinction-cladogenesis” model, which has been widely used by biogeographers. They applied the model to New World “emberizoid” songbirds, a large group of migratory birds that include warblers, cardinals, sparrows, tanagers, and orioles, using a comprehensive phylogenetic tree developed by Keith and a group of colleagues. “We named it the ‘domino model’ because the breeding and winter ranges of species were coded in 3×2 grids of binary values, like dots on domino pieces,” Rick explains. “The computational challenge was to reconstruct the most probable evolutionary shifts from one domino to another.” Examining common ancestors of migratory and non-migratory species over time using the phylogenetic data, the team concluded that there was more evidence supporting the idea that birds lived year-round in North America and began migrating further and further south, resulting in today’s birds migrating thousands of miles every year.

Another result of the study suggests that many tropical species of birds are descendants of migratory ancestors that lost migration and stayed in the tropics year-round. “This is an interesting result because species diversity in this group is much higher in the tropics,” notes Ben. “Previously, more species in the tropics led to the assumption that temperate, migratory species are derived from tropical, non-migratory ancestors; however, the results of our phylogenetic study suggest that the opposite pattern happened often in this group.”

This study received nice coverage by National Geographic, among other outlets, and will soon be featured on the Field’s Science Newsflash web feature.

“Geneticist at work.” In The Field Museum’s Pritzker Lab for Molecular Systematics and Evolution.

So what’s that about botanist and birders joining forces? Well, Ben and Keith are ornithologists, and Rick is a botanist, but with deep experience in biogeography and genomics, which he has applied beyond plants (e.g., butterflies, Amazonian amphibians, lichens). Natural history museums are places where scientists in nominally different fields, but with congruent interests—like biogeography and genomics—can cross paths, and disciplines. Which is one of the things that makes them particularly fascinating places to work.

Here’s the full citation for the article: Benjamin M. Winger, F. Keith Barker, and Richard H. Ree. Temperate origins of long-distance seasonal migration in New World songbirds. PNAS, August 4, 2014 DOI: 10.1073/pnas.1405000111